The rate at which a resting person converts food energy is calledone\'s basal me
ID: 1664027 • Letter: T
Question
The rate at which a resting person converts food energy is calledone's basal metabolic rate (BMR). Assume that the resultinginternal energy leaves a person's body by radiation and convectionof dry air. When you jog, most of the food energy you burn aboveyour BMR becomes internal energy that would raise your bodytemperature if it were not eliminated. Assume that evaporation ofperspiration is the mechanism for eliminating this energy. Supposea person is jogging for “maximum fat burning,”converting food energy at the rate 400 kcal/h above his BMR, andputting out energy by work at the rate 70.0 W. Assume that the heat of evaporation of waterat body temperature is equal to its heat of vaporization at100°C.(a) Determine the hourly rate at which water must evaporate fromhis skin.
1 kg/h
(b) When you metabolize fat, the hydrogen atoms in the fat moleculeare transferred to oxygen to form water. Assume that metabolism of1 g of fat generates 9.00 kcal of energy and produces 1 g of water.What fraction of the water the jogger needs is provided by fatmetabolism?
2%
Explanation / Answer
Can't quite exactly recall what the process is called but in short,you subtract 70W from 400kcal/h to determine how many kg/h of watermust evaporate from his skin. Part A 400kcal = 400,000cal & 1cal = 4.186J (400kcal/hr)(4186J/kcal) = 1674400J/hr 1W = 1J/s. 70W = 70J/s. We need to convert this to J/hr so we: (70J/s)(3600s/hr) =252000J/hr Q = 16474400J/hr - 252000J/hr = 1422400J/hr Heat of Vaporization = 2.26x10^6 Hourly Rate = Q/Heat of Vap = (1422400J/hr)/(2,260,000J/kg) =0.6294kg/hr. Part B Production of 9kcal = 1g water. 400kcal = (400/9)g water =44.44444444g Divide this by the value you found in Part A, which when convertedto grams was = 629.4g and you get: 44.44444444g/629.4g = 0.0706139886 = 7.1% Credits to the anonymous above me for helping me understand partsof the question I didn't before, but also for not getting thenumbers quite right. =(
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